In the recovery of cesium from pollucite and other cesium-containing minerals it is known to digest the mineral ore with an aqueous solution of a strong mineral acid such as hydrochloric or sulfuric acids. When sulfuric acid is used, the cesium may be recovered as cesium alum. Processes for further purification of cesium starting with cesium alum are described in U.S. Pat. Nos. 4,469,670 and 4,466,950.
Alternatively, cesium ore may be roasted in admixture with an alkaline flux to convert the cesium to a water-soluble salt. For example, an alkaline reagent such as calcium oxide or carbonate may be used in combination with a chloride salt such as calcium or sodium chloride, as described in U.S. Pat. No. 4,597,955. The roasted ore then can be extracted with water to obtain an alkaline aqueous solution of cesium chloride together by filtration to obtain a clarified solution of the chlorides.
An important purification step in the process of the above-cited United States patents involves the addition of a water-soluble permanganate, such as potassium permanganate, to a clarified aqueous solution of the metal chlorides. The permanganate selectively precipitates cesium permanganate and other metal ions including aluminum, iron, sodium, potassium, and rubidium remain in solution. The separated cesium permanganate is substantially free of other alkali metal and polyvalent metal compounds. However, one disadvantage of this purification is that large amounts of potassium permanganate are required, a relatively expensive reagent for large-scale processing of cesium ore.
Also, other process steps are required, such as the addition of an alkaline reagent to raise the pH from the low pH of the digest solution, a higher pH being needed to maintain permanganate stability. On the upward adjustment of pH, hydroxide precipitates of aluminum and/or iron may form, and it is necessary to remove these before the solution of metal chlorides is treated with the permanganate. These processing steps are described in U.S. Pat. No. 4,447,406; which, in effect, provides the starting point for the development of the process of this invention. That patent and the other above-cited U.S. patents, as well as the present application, are owned by Carus Corporation of LaSalle, Ill.